Building a Greenhouse for Next to Nothing (Compared to Buying One)

I can’t believe I never did a post about our greenhouse. We’ve now been using it for at least a year and a half and I’ve been oddly silent about it. I guess it’s probably because it’s not 100% complete. We have one small area that still needs a permanent covering, the windows need new glazing and it is in desperate need of new paint. But it’s still functional and gets a lot of use. And it only cost us about $300. $300 may sound like a lot of money until you consider that this greenhouse is 8′x12′ and uses glass glazing. Buying a glass greenhouse that size will generally run you around $5,000.

Why a glass greenhouse? Why not just make a hoop house to save money? Hoop houses are great, don’t get me wrong, but they just don’t stand the test of time. While they are cheaper to make up front, there are some concerns you have to take into consideration. The material usually used for hoop houses is plastic sheeting, which doesn’t last more than a few years, even if it is UV resistant greenhouse plastic film. I’d prefer not to have to add more plastic to the landfill and also spend the money replacing it. Also, special consideration must be made regarding the hoop structure. PVC pipe (most isn’t UV resistant) will degrade the plastic through chemical reaction faster than it would normally degrade, so you have to either wrap the pipe or use another material, like galvanized pipe, which increases the cost. Also, we have a very windy site for most of the year and plastic sheeting just wouldn’t hold up. Polycarbonate greenhouses also degrade from UV but lasts substantially longer than poly film. It is a plastic and even though it my hold up for 10-20 years if properly treated with UV stabilizers, it will discolor and become more opaque after time. It also becomes brittle. Double walled polycarbonate, however, adds a benefit of being more insulating than both glass and film. It can be quite pricey though. Not as expensive as buying glass specifically for a greenhouse, but if you can do glass, which is superior to both film and polycarbonate, for less than either, why wouldn’t you? It’s all about the windows. It is amazing how many people are trying to offload free windows. Craigslist is where we scored the majority of them. We also scored a free door that was 1/2 windows from my best friend who had just bought a house and wanted to replace the front door. We stockpiled old windows until we had what we felt was enough to start building. Before starting we laid out the panes on the ground so we could get the right configuration to fit the walls of the greenhouse. Do this carefully as we had a few casualties while doing this, but fortunately we had enough windows to make up the difference. We made sure that we got some windows with their frames so we could open them as needed when it got hot in the summer. Next, we had to figure out how the greenhouse would be sited. We had a space on the north edge of our property that wasn’t shaded, and it wouldn’t shade out anything. We made the long 12′ wall be the south facing wall to maximize sun exposure. We also decided that since the north facing wall is facing a fence we could just use plywood for it. We framed up the structure with new lumber, which is where a good portion of the money we spent on the greenhouse went towards, however the most costly part of this job was actually the roofing material. We used some of the extra pavers we had to level the structure since our ground slopes. It was also imperative that add extra bracing since the weight of the windows can be quite substantial. The biggest score from the window search were these two 6′ long windows that someone had purchased and then never bothered using. The easily spanned the whole lower half of our south facing wall. It was a tight fit but we got them in. We also got more narrow windows from our next door neighbor that flanked the door (seen in the first photo). Once we got most of the windows in on the south facing wall, we started framing the door and getting the roof joists up. Sexy ain’t it? We decided to just do a simple sloped roof, rather than a gable roof so the south side was getting even more sun exposure, especially in the winter when the sun angle is lower and when we need the greenhouse the most. It’s important when you get the door that it comes with the jamb for easier framing. Once the door was in, we were able to finish up adding windows. And then the roofing, which we used the clear corrugated plastic sheeting. It’s not a particularly pretty greenhouse and it does need a coat of paint, but it’s definitely functional. Of course, what you also have to think about is the interior. Where are you going to put plants? And what about the floor? We scored some pea gravel off of Freecycle and it was enough to put down a nice 3″ layer. We first put down weed cloth though so we wouldn’t be fighting the never ending onslaught of bindweed and Bermuda grass inside. Tom build a fantastic 8′ long potting bench out of scrap wood and then we bought some heavy duty utility “baker” racks for putting the plants on. We will be probably switching the locations of these and put the potting bench on the east facing wall and the racks on the south facing wall so we can add another one. We also are using an old unused compost bin (our chickens do all of our composting now) as a soil storage.

Hi Sue! It all kind of depends on where you live and your climate. Here in Vallejo, CA we don’t need a heat source in the winter and opening up the windows in the summer is fine for keeping plants in it. We grew peppers in it last year all summer, but there isn’t any automatic irrigation in there and I’m not one to keep up on hand watering with all the other stuff we do so I didn’t keep them going this year.

And yes, the windows are all framed have 2x4s that they are screwed onto.

rbrink21 I am south of the equator in OZ but have to have some sort of heat to keep summer things going in winter.
Our frosts this winter have only been down to -5C but I still have tomatoes, chillies, capsicums and eggplants alive. Also some “seedling” potatoes which I will be planting out in about 6 weeks.
Up to last couple of years a frost just below zero would do untold damage in my poly tunnels. The past couple of years I added a 400Lt water tank in one (they are side by side) and was able to keep things well to about -4C but destroyed at about -6C. Then this year I added a second tank (they are painted with flat black paint) in the other hothouse but haven’t had the really bad temperatures to see how low they can go ( don’t want them that cold either).
The sun shining on the tanks during the day warm up then slowly release their heat over night to temper the cold from outside.
The hothouses are surrounded by shadecloth and another piece over the top to reduce the effects of frost too.
Sometime in the future I will either add a couple of recycled solar collectors to heat the water or may be do some other work to trap warm inside to be released at night time.